1. Field of the Invention
The present invention relates to windows.
2. Description of the Related Art
Natural light is generally preferable to artificial light for lighting workspaces and homes during the day. The spectrum of natural light has a warm, pleasant quality. Plentiful natural light helps a room to feel larger and less confined, and enhances the mood of people working or relaxing in the room. Natural light has the disadvantage of being variable and sometimes unpredictable. On a warm day, sunlight pouring in through a window can quickly overheat a room. The amount of light entering a room can be controlled with curtains and blinds. However, these have to be manually adjusted when the light level changes. Closed shades, curtains, and blinds also obscure the view through the window.
Too much light entering through a window also causes glare. Glare is a particular problem with screens, such as television screens and computer screens. Glare makes the contents of the screen hard to see, and can lead to eyestrain and fatigue. The larger the screen, the more of a problem glare is. Big-screen televisions, including projection televisions, are particularly prone to annoying glare problems.
Curtains, blinds, and the like often allow small amounts of light to pass through them, even when completely closed. For example, light may leak around the edges of a shade or between the slats of a blind. This light can cause annoying lines of glare on a screen.
Anti-glare covers for computer screens are available to control the problem of glare. The cover is located between the user's eyes and the screen and can itself interfere with the user's view of the screen.
Windows suited for use in homes and other buildings are available in a wide variety of shapes, sizes, and glass types. Thermal windows having multiple panes of glass separated by a sealed space are well known. The most common type contains two panes of glass and is referred to as a double-glazed or double-pane window. The panes are ordinarily separated by a space of about 3/16 to 5/8 inch. The space reduces heat loss. Typical thermal window panes are made of clear glass. The space may be filled with air or another gas, such as carbon dioxide, argon, or krypton.
It is known to use low-emissivity or low-E glass in thermal windows. Low-E glass has a thin, clear coating of a metal oxide. The coating allows most of the visible light to pass through, but is a barrier to longer infrared and near-infrared wavelengths. In winter, sunlight passes through to warm the surfaces in a room, but the heat which re-radiates is blocked from escaping. In summer, low-E glass blocks heat radiated from outdoor surfaces from entering the house. Low-E glass also partially blocks ultraviolet or UV radiation.
The use of tinting to limit visible light passing through a window is well known. Common types are gray-tinted and bronz-tinted windows. Tinted windows block light regardless of the weather conditions. A tint dark enough to control glare on a bright, sunny day is likely to be unpleasantly dark on cloudy days or when the sun is low in the sky.
Photochromic glass which darkens in response to light is well known. Photochromic glass is frequently used as lens material for eyeglasses and sunglasses. A photochromic lens material is commercially available under the trademark "PHOTOGRAY EXTRA" from Corning Glass Works. The most common types of photochromic materials change color when the incident radiation causes a lower-energy form of a photochromic molecule to change into a higher-energy form with a different absorption spectrum.
U.S. Pat. No. 3,964,823 to Trozzolo discloses articles employing photochromic materials and is incorporated by reference. The photochromic materials include mono- and bicyclic aziridines and bi- and tri-cyclic oxirane compounds in crystalline form. The photochromic materials function by selective absorption depending on the polarization of the incident radiation. This is particularly effective in selectively reducing reflected or glare light. The articles include windshields, glass panes, and sunglasses.
U.S. Pat. No. 4,608,349 to Kerko et al. disclose photochromic glass compositions and is incorporated by reference The photochromic glass compositions are stated to be suitable for thin, refractive-index-corrected lightweight lenses.
U.S. Pat. No. 5,390,045 to Bernard, Jr. teaches a selectively variable window tinting system for limiting the passage of visible light and radiative heat through an automobile window. In a first embodiment, the system includes automobile glass made of a photochromic glass which darkens on exposure to sunlight. In a second embodiment, the system has a pair of glass panes. A tinted fluid can be pumped in and out between the panes. Two or more fluids can be used so that the degree of tint can be changed. The system is stated to be suitable for house windows.
None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed. Thus a light-reactive thermal window solving the aforementioned problems is desired.